A heat recovery steam generator (“HRSG”) is a device that may include one or more ducts through which hot gas may be used by heat exchangers to transfer heat from the hot gas to a fluid. Examples of heat exchanges may be found in U.S. Patent Application Publication Nos. 2013/0186594, 2013/0180471, 2013/0192810, 2012/0240871, 2011/0239961 and 2007/0119388 and U.S. Pat. Nos. 3,756,023, 4,932,204, 5,881,551, 6,173,679, and 7,481,060.
Known vertical HRSG evaporators include horizontal evaporator tubes that can have instabilities during evaporator start-up operations. The evaporators can feed steam and heated liquid water to a steam drum, which also can experience water level instabilities during start-up operations. Recirculation pumps can address such instabilities by preventing a reverse flow, or back-flow, of steam to the steam drum. Such a feature can also address a water hammer condition, which can require the evaporators to be shut down. Recirculation pumps can impact operational and maintenance costs.